Modular electric generator for variable speed turbines

ABSTRACT

An electric power generation system may be constructed of multiple similar generator modules arranged between a rotor and a stator. The rotor may be coupled to and/or integrated with a turbine that is configured to rotate in the presence of a fluid stream such as wind or water. Each generator module may have a rotor portion configured to generate a magnetic field having at least one characteristic that changes with respect to the rotational speed of the rotor. Each generator module may further have a stator portion configured to generate an alternating electric current responsive to the magnetic field. The generated electric current may be controlled by the stator portion of the generator module in order to magnetically control the rotational speed of the rotor and the turbine. Separation between the rotor and stator portions of the generator module may be magnetically maintained.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Continuation-in-Part of co-pending U.S.application Ser. No. 11/960,605 (Attorney Docket No. 026599-000310US),filed Dec. 19, 2007, which claims the benefit of U.S. ProvisionalApplication No. 60/870,886, filed Dec. 20, 2006, the full disclosures ofwhich are incorporated herein by reference. This application also claimsthe benefit of U.S. Provisional Application No. 61/310,234 (AttorneyDocket No. 028442-000100US) filed on Mar. 3, 2010, and U.S. ProvisionalApplication No. 61/414,732 Attorney Docket No. 028442-000200US) filed onNov. 17, 2010, the full disclosures of which are also incorporatedherein by reference.

BACKGROUND

From lighting and heating to electrolysis and electric motors, electricpower is employed in an ever increasing number of applications inresidential, commercial and industrial sectors. This demand for electricpower is met by a wide variety of electric power generation systems(“generation systems”) including coal and gas-fired power plants,nuclear power plants, hydroelectric power stations and wind turbines.However, conventional generation systems have disadvantages. Forexample, some conventional generation systems consume nonrenewable fuelsand/or have adverse environmental impacts such as associated pollutionand/or hazardous waste. Some conventional generation systems avoid thesedisadvantages, but have other shortcomings.

For example, some conventional generation systems generate electricpower based on renewable fluid streams such as wind, renewable waterflows including tidal and wave-associated water flows, and geothermallyheated fluid streams. Such renewable fluid streams may be naturallyoccurring or naturally assisted, and may have characteristics such asflow rate and power density that vary significantly and/or depend ongeographic location. Such variability of fluid stream characteristicscan present a challenge to designers of conventional generation systems,and some conventional generation systems are designed to operateefficiently and/or effectively only within a relatively narrow range ofcharacteristic values. For example, wind quality available at differentgeographical locations may be classified by average power density orwind speed, and conventional wind turbines may require particularclasses of wind to operate efficiently and/or effectively. Suchlimitations on conventional generation system designs may significantlyconstrain the geographical regions suitable for the generation systemsand/or be associated with significant electric power transmission costs.

Some conventional generation systems attempt to expand the range ofoperationally suitable characteristic values by incorporating variablepitch turbines. However, variable pitch turbines can be significantlymore expensive and/or less reliable than fixed pitch turbines. Someconventional generation systems attempt to expand the range ofoperationally suitable characteristic values by incorporating amechanical gearbox. However, such gearboxes can be a significant portionof the purchase and/or maintenance cost of the system. Some conventionalgeneration systems are custom manufactured to perform efficiently and/oreffectively with respect to expected ranges of characteristic values atparticular geographical locations. However, such custom manufacture canbe significantly more expensive and/or require significantly longer tomanufacture and/or maintain relative to designs amenable to massproduction techniques.

SUMMARY

An electric power generation system may be constructed of multiplesimilar generator modules arranged between a rotor and a stator. Therotor may be coupled to and/or integrated with a turbine. The turbinemay be configured to rotate in the presence of a fluid stream such aswind or water. A rotational speed of the turbine may vary depending on aflow rate of the fluid stream. A rotational speed of the rotor maycorrespond to the rotational speed of the turbine. The coupling of theturbine and rotor need not include a mechanical gearbox configured tomediate the rotational speed of the rotor with respect to the rotationalspeed of the turbine. Each generator module may have a rotor portioncoupled to the rotor and configured to generate a magnetic field havingat least one characteristic that changes with respect to the rotationalspeed of the rotor. Each generator module may further have a statorportion coupled to the stator and configured to generate an alternatingelectric current responsive to the magnetic field. The generatedelectric current may be controlled by the stator portion of thegenerator module in order to magnetically control (e.g., decelerate) therotational speed of the rotor and the turbine. Separation between therotor and stator portions of the generator module may be magneticallymaintained.

As part of magnetically controlling the rotational speed of the rotorand turbine, values of one or more characteristics of the rotor and/orgenerated electric current may be measured. Target values for thosecharacteristics may be determined. For example, particular target valuesof the generated electric current may correspond to particularrotational speeds of the rotor and/or the turbine. An optimal value ofthe rotational speed of the turbine may exist with respect to a givenflow rate of the fluid stream. Target values of the characteristics ofthe generated electric current may be selected to correspond to theoptimal value of the rotation speed of the turbine. The generatormodules of a generator may act individually and/or collectively toachieve the target values.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used asan aid in determining the scope of the claimed subject matter. Otherobjects and/or advantages of the present invention will be apparent toone of ordinary skill in the art upon review of the detailed descriptionof the present invention and the included figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which:

FIG. 1 is a cross-sectional diagram depicting aspects of an exampleelectric generator in accordance with some embodiments of the presentinvention;

FIG. 2 is a cross-sectional diagram depicting aspects of another exampleelectric generator in accordance with some embodiments of the presentinvention;

FIG. 3 is a cross-sectional diagram depicting aspects of still anotherexample electric generator in accordance with some embodiments of thepresent invention;

FIG. 4 is a cross-sectional diagram depicting aspects of yet anotherexample electric generator in accordance with some embodiments of thepresent invention;

FIG. 5 is a cross-sectional diagram depicting aspects of a furtherexample electric generator in accordance with some embodiments of thepresent invention;

FIG. 6 is a cross-sectional diagram depicting aspects of still anotherexample electric generator in accordance with some embodiments of thepresent invention;

FIG. 7 is a cross-sectional diagram depicting aspects of still yetanother example electric generator in accordance with some embodimentsof the present invention;

FIG. 8 is a cross-sectional diagram depicting aspects of an examplegenerator module in accordance with some embodiments of the presentinvention;

FIG. 9 is a cross-sectional diagram depicting aspects of another examplegenerator module in accordance with some embodiments of the presentinvention;

FIG. 10 is a cross-sectional diagram depicting aspects of an exampleretrofitted electric generator in accordance with some embodiments ofthe present invention;

FIG. 11 is a cross-sectional diagram depicting aspects of an exampletower-mounted electric power generation system in accordance with someembodiments of the present invention;

FIG. 12 is a schematic diagram depicting aspects of an example powerelectronics submodule in accordance with some embodiments of the presentinvention;

FIG. 13 is a schematic diagram depicting aspects of an example generatedAC management network in accordance with some embodiments of the presentinvention;

FIG. 14 is a schematic diagram depicting aspects of an example generatormodule plate stack in accordance with some embodiments of the presentinvention;

FIG. 15 is a flowchart depicting example steps for generating electricpower in accordance with some embodiments of the present invention;

FIG. 16 is a flowchart depicting example steps for configuring generatormodules in accordance with some embodiments of the present invention;and

FIG. 17 is a flowchart depicting further example steps for configuringgenerator modules in accordance with some embodiments of the presentinvention.

Note that the same numbers are used throughout the disclosure andfigures to reference like components and features.

DETAILED DESCRIPTION

In an embodiment of the invention, mass produced generator modules maybe arranged between a rotor and a stator to generate electric power.Electric generators of widely varying sizes and/or capacities (e.g., 100kW to 20 MW) may be constructed with different numbers of the generatormodules and, optionally, larger rotor and/or stator frames. Thegenerator modules may be arranged in rings and/or layers, radiallyand/or axially. The rotor frame may be coupled to a turbine configuredto rotate in a fluid stream. For example, the fluid stream may be arenewable fluid stream having variable characteristics such as wind, andthe turbine may be a fixed pitch turbine. An electric generatorincorporating the generator modules may adapt to changes in a rotationalspeed of the turbine and/or a corresponding torque resulting from thefluid stream with a magnetically-induced counter-torque and without useof a mechanical gearbox.

Each generator module may have a rotor portion (“rotor module”) coupledto the rotor frame and a stator portion (“stator module”) coupled to thestator frame. Separation of the rotor modules and the stator modulesduring rotation of the rotor may be maintained substantially withmagnetic bearings. Each generator module may include a polyphasealternating current (AC) generator coil and a power electronicssubmodule configured at least to modify the generated electric voltageand/or current waveforms so as to maintain the rotational speed of theturbine at a desired and/or optimal value with respect to a flow rate ofthe fluid stream and the capabilities of the generator. The generatormay incorporate a central controller to coordinate the power electronicsof the generator modules and/or the generator modules may actindependently. The generator modules may be hot-swapped for maintenancepurposes. For example, the generator modules of the generator maycollectively adapt to an unexpected failure, hot-unplug and/or hot-plugof one or more of the generator modules.

An axis of rotation of the turbine may be horizontal or vertical. Anaxis of rotation of the coupled rotor frame and the rotor modules maycorrespond to the axis of rotation of the turbine or be arrangedperpendicularly. Larger capacity generators (e.g., greater than 10 MW)may be possible when the rotor frame has a vertical axis of rotation.Conventional electric power generator structures may be retrofitted withgenerator modules to obtain one or more benefits in accordance with anembodiment of the invention. A retrofitted electric power generatorstructure may have an expanded dynamic range with respect to fluidstream flow rates at which the retrofitted system can operateefficiently and/or effectively. For example, a retrofitted wind turbinemay operate effectively at lower wind power densities (e.g., less than400 Watts per square meter) as well as at higher wind power densities(e.g., greater than 1000 Watts per square meter) and during wind bursts.

FIG. 1 is a cross-section of an example electric generator 100 inaccordance with an embodiment of the invention. FIG. 1 is not to scaleand omits structural elements for clarity. The electric generator 100may incorporate a turbine 102 having a horizontal axis of rotation 104that rotates in the presence of a fluid stream 106. For example, thefluid stream 106 may be air, and the turbine may incorporate one or moreairfoil shaped blades. The cross-section of FIG. 1 is from a point ofview perpendicular to the axis of rotation 104. The rotational speed ofthe turbine 102 may vary depending a flow rate of the fluid stream 106.That is, the turbine 102 may be configured as a variable speed turbine.The turbine 102 may be coupled to a rotor 108 that incorporates multiplerotor modules 110-112. The rotor 108 may rotate within a stator 114 thatincorporates multiple stator modules 116-118. Separation 120 between therotor 108 and the stator 114 may be magnetically maintained, forexample, with magnetic bearings. The magnetically maintained separation120 can enable very low losses due to friction, as well as enablinggeneration of electric power when fluid stream 106 flow rates arerelatively low including flow rates at which conventional electric powergeneration systems would perform sub-optimally or not at all (e.g.,below conventional “cut-in” flow rates). The rotor diameter 122 may berelatively large with respect to diameters of rotors in conventionalelectric power generation systems.

For clarity, the example of a wind power generation system will be usedthroughout this description. However, each embodiment of the inventionis not limited to this example. The fluid stream 106 may be a flow ofany suitable fluid including suitable gases such as air and steam, aswell as suitable liquids such as water. The term “fluid” is used hereinin the technical sense of fluid dynamics, and is not limited to liquids.The mass of the rotor may be concentrated in the rotor modules 110-112,however, the rotor modules 110-112 need not have the proportions withrespect to the rotor 108 depicted in FIG. 1. As described below in moredetail with reference to FIG. 8 and FIG. 9, the rotor modules 110-112need not be embedded within the rotor 108, and the stator modules116-118 need not be embedded within the stator 114.

FIG. 2 is a cross-section of another example electric generator 200 inaccordance with an embodiment of the invention from an illustrativeperspective different from that of FIG. 1. FIG. 2 is not to scale andomits structural elements for clarity. The electric generator 200includes a rotor 202 rotating about an axis of rotation 204 within astator 206. The cross-section of FIG. 2 is from a point of view parallelto the axis of rotation 204. The rotor 202 includes multiple rotormodules 208-218 arranged in a ring. The stator 206 includes multiplestator modules 220-230 arranged in a corresponding ring. The ellipses “. . . ” between the rotor modules 208 and 218 and between the rotormodules 212 and 214 indicate that the rotor 202 may include any suitablenumber of rotor modules. Ellipses throughout the drawings have a similarmeaning. The rotor modules 208-218 are examples of the rotor modules110-112 of FIG. 1. The stator modules 220-230 are examples of the statormodules 116-118 of FIG. 1. In an embodiment of the invention, the ratioof rotor modules 208-218 to stator modules 220-230 is one-to-one (1:1),however, each embodiment of the invention is not so limited.

The electric generators 100 and 200 of FIG. 1 and FIG. 2 have rotors 108and 202 nested within their respective stators 114 and 206. However,each embodiment of the invention is not so limited. FIG. 3 is across-section of still another example electric generator 300 inaccordance with an embodiment of the invention. FIG. 3 is not to scaleand omits structural elements for clarity. The electric generator 300includes components 302, 308, 310-312, 314 and 316-318 corresponding tothe components 102, 108, 110-112, 114 and 116-118, respectively, of theelectric generator 100 of FIG. 1. However, the arrangement of thecomponents 302, 308, 310-312, 314 and 316-318 is different. In theelectric generator 300, the rotor 308 and rotor modules 310-312 may becoupled to and/or integrated with radial extremities of blades of theturbine 302. A hub 324 of the turbine 302 may be coupled with the stator314, and may incorporate axial and/or radial bearings. Nevertheless, theseparation 320 between the rotor 308 and the stator 314 may besubstantially magnetically maintained, for example, with magneticbearings incorporated into the rotor modules 310-312 and the statormodules 316-318.

When an axis of rotation 304 of the turbine 302 is horizontal (e.g.,perpendicular to a local direction of gravitational force),gravitational loading can increase peak stress in particular portions ofthe generator 300. In an embodiment of the invention, peak stress can bereduced, and thus larger form factors and/or system capacities achievedwith same cost materials, by utilizing a rotor with a vertical axis ofrotation. FIG. 4 is a cross-section of yet another example electricgenerator 400 in accordance with an embodiment of the invention. FIG. 4is not to scale and omits structural elements for clarity. The electricgenerator 400 includes components 402, 408, 410-412, 414 and 416-418corresponding to the components 302, 308, 310-312, 314 and 316-318,respectively, of the electric generator 300 of FIG. 3. In addition, theelectric generator 400 includes a gearbox 424 suitable for transferringa torque generated by the turbine 402 rotating around a horizontal axis426 to a vertical axis of rotation 428 of the rotor 408. The gearbox 424need not adjust rotational speed, so that a rotational speed of therotor 408 may correspond to a rotational speed of the turbine 402.

Alternatively, the gearbox 424 may be eliminated by incorporating aturbine that rotates around the vertical axis 428 in the presence of afluid stream 406. FIG. 5 is a cross-section of a further exampleelectric generator 500 in accordance with an embodiment of theinvention. FIG. 5 is not to scale and omits structural elements forclarity. The electric generator 500 includes components 508, 510-512,514 and 516-518 corresponding to the components 408, 410-412, 414 and416-418, respectively, of the electric generator 400 of FIG. 4. However,the electric generator 500 incorporates turbine blades 524 oriented soas to cause rotation around a vertical axis 504 when in the presence ofa fluid stream 506. In the example electric generator 500, the turbineblades 524 are fastened directly to the rotor 508, and so cause therotor 508 to rotate around the vertical axis 504. However, eachembodiment is not so limited, and the turbine blades 524 and/or aturbine frame (not shown in FIG. 5) may be connectively coupled to therotor 508 in any suitable manner. Furthermore, the turbine blades 524need not have the number or arrangement depicted in FIG. 5, but mayinclude any suitable number of blades (including one) and may bearranged in any suitable configuration that causes rotation around thevertical axis 504 including configurations corresponding to those foundin Darrieus wind turbines and Savonius wind turbines known to those ofskill in the art.

In the example generators 100, 200, 300, 400, 500 of FIGS. 1-5, theseparation between the rotors and the stators is depicted as beingmaintained with respect to a single rotor and/or stator surface.However, each embodiment of the invention is not so limited. FIG. 6 is across-section of still another example electric generator 600 inaccordance with an embodiment of the invention. FIG. 6 is not to scaleand omits structural elements for clarity. As in the electric generator400 of FIG. 4, the electric generator 600 includes a rotor 608 thatincorporates multiple rotor modules 610-612. However, the electricgenerator 600 incorporates a stator 614 having a shape that requiresseparation between the stator 614 and the rotor 608 to be maintainedwith respect to multiple surfaces. The electric generator 600 furtherincludes multiple sets of stator modules (e.g., a set of lower statormodules 624-626 and a set of upper stator modules 628-630) to maintainthe separation. Such an arrangement may provide for greater separationstability, for example, in response to transient and/or stochasticperturbing forces and/or torques incident upon the rotor 608.

Referring back to FIG. 1, the set of rotor modules 110-112 together withthe set of stator modules 114-116 is collectively called a set, ring orplate of generator modules 110-116. In accordance with an embodiment ofthe invention, an electric generator may include multiple sets ofgenerator modules. FIG. 7 is a cross-section of still yet anotherexample electric generator 700 in accordance with an embodiment of theinvention. FIG. 7 is not to scale and omits structural elements forclarity. The electric generator 700 includes a rotor 708 thatincorporates multiple sets of rotor modules 724-726, 728-730 and 732-734rotating around a common axis 704. The rotor 708 rotates within a stator714 that incorporates multiple sets of stator modules 736-738, 740-742and 744-746. Each plate of generator modules may correspond to the plateof generator modules 110-116 of FIG. 1. High capacity electricgenerators can be constructed from “stacks” of such plates, for example,as described below in more detail with reference to FIG. 14.

The description now turns to generator module components in accordancewith an embodiment of the invention. FIG. 8 is a cross-section of anexample generator module 800 in accordance with an embodiment of theinvention. FIG. 8 is not to scale and omits structural elements forclarity. The generator module 800 includes a rotor module 802 and astator module 804 having a magnetically maintained separation 806.

The rotor module 802 may incorporate a set of magnetic bearings (e.g.,magnetic bearing 808 and like shaded components in FIG. 8) fastened to arotor module frame 810 and configured at least in part to maintain theseparation 806 between the rotor module 802 and the stator module 804.The rotor module 802 may further incorporate a field magnet 812connectively coupled to the rotor module frame 810. A magnetic fieldkeeper 814 may be inserted between the field magnet 812 and the rotormodule frame 810 and configured at least in part to maintain themagnetic field generated by the field magnet 812.

The stator module 804 may also incorporate a set of magnetic bearingsfastened to a stator module frame 816 and configured at least in part tomaintain the separation 806 between the rotor module 802 and the statormodule 804. The set of magnetic bearings fastened to the rotor moduleframe 810 and the set of magnetic bearings fastened to the stator moduleframe 816 may interact and cooperate to maintain the separation 806. Thestator module 804 may further include a generation coil 818 configuredat least to generate polyphase (e.g., 3 phase) alternating electriccurrent (AC) responsive to a time-varying magnetic field generated atleast in part by the field magnet 812. The field magnet 812 mayincorporate a set of permanent magnets arranged so as to generate thepolyphase alternating electric current in the generation coil 818 as therotor module 802 is rotated past the stator module 804. The field magnet812 may incorporate any suitable type of permanent magnet. The statormodule frame 816 may incorporate a magnetic core 820 configured at leastto enhance a performance of the generation coil 818. For example, themagnetic core 820 may include laminated back-iron and/or ferrite.

The components of the generator module 800 may have manufacturingtolerances such that the separation 806 may be relatively small, forexample, on the order of millimeters. This can be significant withrespect to sizing and selecting generator module 800 componentsincorporating permanent magnets because of the strong dependence ofmagnetic force on distance, as will be apparent to one of skill in theart.

FIG. 9 is a cross-section of another example generator module 900 inaccordance with an embodiment of the invention. FIG. 9 is not to scaleand omits structural elements for clarity. The generator module 900incorporates components 902, 904, 908, 910, 912, 916, 918 and 920corresponding to components 802, 804, 808, 810, 812, 816, 818 and 820,respectively, of the generator module 800 of FIG. 8, althoughdifferently arranged. Each generator module 900 may have smallassociated mass and be removed and serviced of other components of thegenerator 100 (FIG. 1). In the generator module 900 of FIG. 9, themagnetic bearings (e.g., components shaded like the magnetic bearing908) may be sized and/or selected independently from a sizing and/orselection of the field magnet 912 and/or the generator coil 918. Thefield magnet 912 may be connectively coupled to the rotor module frame910 with a flexible coupling 922 that provides the field magnet 912 witha freedom to move in a direction parallel with a main magnetic fluxpath, for example, in the axial direction and/or the radial directionwith respect to the axis of rotation 104 (FIG. 1). The flexible coupling922 may further provide the field magnet 912 with a degree of isolationfrom vibrations in the rotor module frame 910.

A physical separation between the field magnet 912 and the generationcoil 918 may be maintained and/or stabilized (collectively,“stabilized”) at least in part by a set of stabilization magnets (e.g.,stabilization magnet 924 and like shaded components in FIG. 9). Theseparation stabilization may be assisted by a set of stabilization coils926-928. Such separation stabilization may create a magnetic well thattightly controls a relative position of the field magnet 912 (e.g., withrespect to the generation coil 918). In an embodiment of the invention,the configuration of the generator module 900 allows for the rotormodule 902 to move past the stator module 904 at a wide variety ofspeeds.

The polyphase alternating electric current (the “AC waveform”) generatedin the generation coil 918 by the passage of the rotor module 902 may bemanaged by a power electronics submodule 930. In an embodiment of theinvention, the relative speed of the rotor module 902 with respect tothe stator module 904, and thus the generated AC waveform, dependsdirectly on a rotational speed of the turbine 102 (FIG. 1) to which therotor module 902 is coupled. The power electronics submodule 930 mayconvert the generated AC waveform into an AC waveform in accordance withlocal power grid specifications. By managing the AC waveform in thegeneration coil 918 (e.g., with respect to amplitude, frequency and/orphase), the power electronics submodule 930 may influence a motion ofthe rotor module 902 and the structures to which the rotor module 902 isconnectively coupled such as the turbine 102. For example, the powerelectronics submodule 930 may act to adjust (e.g., decelerate oraccelerate) a rotational speed of the turbine 102 to perform optimallywith respect to one or more characteristics (e.g., flow rate, fluiddensity) of the fluid stream 106. An example power electronics submodule930 in accordance with an embodiment of the invention is described belowin more detail with reference to FIG. 12.

Each generator module 900 may have small associated mass and be removedand serviced independent of other components of the generator 100 (FIG.1). The generator module 900 may further include one or more active orpassive thermal regulation components (not shown in FIG. 9). Thegenerator module 900 may utilize any suitable thermal regulationtechnology including air or liquid cooling. Each generator module 900may include sufficient thermal regulation capacity to regulate itselfindependent of other components of the generator 100.

In an embodiment of the invention, conventional electric powergeneration system structures may be retrofitted with generator modules900. FIG. 10 is a cross-section of an example retrofitted electric powergenerator 1000 in accordance with an embodiment of the invention. FIG.10 is not to scale and omits structural elements for clarity. Theretrofitted electric power generator 1000 may incorporate multiple setsof generator modules arranged between a rotor frame 1002 and a statorframe 1004. In FIG. 10, generator module arrangement and/orconfiguration is depicted with generator module symbol 1006. Forexample, each such generator module symbol may correspond to thegenerator module 900 of FIG. 9. As depicted in FIG. 10, sets ofgenerator modules may be layered axially and nested radially to fit adesired form factor. Although the magnetic bearings of the generatormodules may act as the main bearings of the generator 1000, thegenerator 1000 may incorporate a thrust bearing 1008 to facilitaterotation of the rotor frame 1002. Salvaged turbine blades (not shown inFIG. 10) may be reused, recycled and/or retrofitted to the generator1000 at least in part by connectively coupling the salvaged turbineblades to the rotor frame 1002 with a retrofit hub 1010 and/or retrofithub adapter 1012.

Each of the rotor frame 1002, the stator frame 1004, the retrofit hub1010 and the retrofit hub adapter 1012 may be composed of segmentscapable of being transported through constrained areas and assembled inthe field. For example, these components may each have segmentsdetermined according to a 3-fold rotational symmetry of the generator1000. If the generator 1000 incorporates a shroud such as a nacelleshroud (not shown in FIG. 10), the shroud may be similarly segmented. Asan alternative to the retrofit hub 1010 and the retrofit hub adapter1012, corresponding original equipment may be connectively coupled tothe rotor frame 1002.

In an embodiment of the invention, the power electronics submodule 930of the generator module 900 (FIG. 9) may be configured to allow thegenerator submodule 900 to act both as an electric generator and anelectric motor. As well as influencing motion of the turbine 102 (FIG.1), sets of generator modules may be arranged to provide for yaw controlof the turbine 102 and thus adapt to changes in direction of the fluidstream 106. FIG. 11 is a cross-section of an example tower-mountedelectric power generation system 1100 in accordance with an embodimentof the invention. FIG. 11 is not to scale and omits structural elementsfor clarity.

A generator 1102 (e.g., corresponding to the generator 1000 of FIG. 10)may be connectively coupled to a tower 1104 with a tower adapter 1106.In an embodiment of the invention, the tower adapter 1106 may be asimple fixed coupling, and yaw control of the turbine 1108 with respectto the fluid stream 1110 may be enabled by a set of generator modules1112 arranged between a swiveling base 1114 of the tower 1104 and afixed base 1116 of the tower 1104. The fixed based 1116 may be attachedto a suitable foundation embedded in a suitable geologic surfaceincluding hill tops, hill sides, river beds and ocean beds. Thegenerator modules 1112 may act as main bearings for the tower 1104 andbe configured as motors to rotate the tower 1104 about an axis 1118responsive to changes in a direction of the fluid stream 1110. In thiscase, and when larger rotational diameters are available to achievehigher tangential velocities (e.g., in other cases where there is avertical axis of rotation), the magnetic bearings of the generatormodule 900 (FIG. 9) may be replaced and/or supplemented with passivemagnetic levitation (“passive maglev”). The tower 1104 may beairfoil-shaped to reduce shock experienced by turbine 1108 blades asthey rotate past the tower 1104.

The power electronics submodule 930 (FIG. 9) of the generator module 900plays a significant role in the performance of the generator module 900.FIG. 12 is a schematic diagram of an example power electronics submodule1202 in accordance with an embodiment of the invention. A polyphasealternating electric current generation coil 1204 (e.g., the generationcoil 918 of FIG. 9) may be tapped at multiple points 1206-1208 enablingthe coil 1204 to adapt to significant variation in rotor module 902speed. In an embodiment of the invention, this enables electric powergeneration system design flexibility with respect to location of therotor module 902 at different distances from the axis of rotation (e.g.,as in the generator 1000 of FIG. 10). The power electronics submodule1202 may include corresponding electronically controlled sets of coiltap selection switches 1210-1212 that enable the power electronicssubmodule 1202 to select an appropriate coil tap point.

The AC waveform generated in the polyphase coil 1204 may be presented toan active rectifier 1214. The active rectifier 1214 may be astandardized and easily replaceable component of the power electronicssubmodule 1202. In an embodiment of the invention, the coil tapselection switches 1210-1212 may be incorporated into the activerectifier 1214 and/or the active rectifier 1214 may incorporatecorresponding power routing to distinct sets of subcomponents designedto manage AC waveforms with different characteristics (e.g., withrespect to amplitude and frequency). The active rectifier 1214 mayrectify the AC waveform into a direct electric current (DC). The activerectifier 1214 may have multiple DC outputs 1216-1218, for example,corresponding to different voltage and/or current levels. The powerelectronics submodule 1202 may incorporate corresponding electronicallycontrolled sets of DC power bus selection switches 1220-1222 that enablethe electronics submodule 1202 to select an appropriate DC powerrouting.

The DC power output by the active rectifier 1214 may be routed to aninverter 1224. The inverter 1224 may be a standardized and easilyreplaceable component of the power electronics submodule 1202. In anembodiment of the invention, the DC power bus selection switches1220-1222 may be incorporated into the inverter 1224 and/or the inverter1224 may incorporate corresponding power routing to distinct sets ofsubcomponents designed to manage DC power with different characteristics(e.g., with respect to voltage and/or current levels). The inverter 1224may transform the routed DC power into a polyphase AC waveform 1226 inaccordance with local power grid specifications (“grid-quality AC”).

The active rectifier 1214 and/or the inverter 1224 may be configuredand/or controlled by a submodule controller 1228 capable of acting inaccordance with command messages and/or signals sent over a data bus1230 to the power electronics submodule 1202. For example, the data busmay be optical fiber or shielded twisted pair (STP). The submodulecontroller 1228 may include a communication component 1232 capable ofparticipating in sophisticated communication protocols such as internetprotocols. The communication component 1232 may route command messagesand/or signals to a rectifier controller 1234 and/or an invertercontroller 1236 as appropriate. Alternatively, the communicationcomponent 1232 may translate received command messages and/or signals toforms (e.g., simpler forms) suitable for the rectifier controller 1234and/or the inverter controller 1236. The rectifier controller 1234 andthe inverter controller 1236 may translate received command messagesand/or signals into command messages and/or signals suitable forcontrolling the active rectifier 1214 and the inverter 1224,respectively, and/or generate suitable such command messages and/orsignals.

For example, the communication component 1232 may receive an internetprotocol (IP) message or datagram specifying a current flow rate of thefluid stream 106 (FIG. 1) using Unicode characters. In response, thecommunication component 1232 may generate a signal voltage over acontroller signaling path 1238 to the rectifier controller 1234 that hasa level corresponding to the received current flow rate. In response tothe signal voltage, the rectifier controller 1234 may generate apulse-width modulation (PWM) signal 1240 suitable for controlling theactive rectifier 1214.

As another example, the communication component 1232 may receive one ormore signals corresponding to a rotational speed, and/or othercharacteristic, of the rotor 108 (FIG. 1) and/or the turbine 102. Inresponse, the communication component 1232 may relay the one or moresignals over a controller signaling path 1238 to the rectifier control1234. Alternatively, the stator module 904 (FIG. 9) may include one ormore sensors (not shown in FIG. 9) configured to generate suitable suchsignals, freeing the communication component 1232 for other tasks.

In an embodiment of the invention, the power electronics submodule 1202integrated into the generator module 900 (FIG. 9) includes the activerectifier 1214 and the inverter 1224 and outputs grid-quality AC.However, in alternative embodiments, components of the power electronicssubmodule 1202 may be differently distributed throughout the electricpower generation system (e.g., the electric power generation system1100). For example, in one alternative, the components above the dashedline 1242 may be incorporated in each generator module 900, and thenmultiple DC power buses 1216-1218 and a data bus 1230 and/or signalingbus 1238 routed to an inverter 1224 and submodule controller 1228assigned to multiple generator modules. In another alternative, thecomponents below the dashed line 1244 may be located remotely from thegenerator modules with the appropriate power and signaling routing.

In an embodiment of the invention, single power electronics submodulesmay be configured to manage an AC waveform generated by multiplegeneration coils such as the polyphase coil 1204. FIG. 13 is a schematicdiagram of an example generated AC management network 1300 in accordancewith an embodiment of the invention. Multiple polyphase generation coils1302-1306 (such as polyphase generation coil 918 of FIG. 9) may beconnected to an inter-coil AC bus 1308. The inter-coil AC bus 1308 mayincorporate coil selection switches 1310-1316 enabling selection,isolation, partition and/or grouping of particular sets of generationcoils 1302-1306. Similarly, multiple power electronics modules 1318-1320(such as power electronics submodule 930) may be connected to aninter-module AC bus 1322. The inter-module AC bus 1322 may incorporatemodule selection switches 1324-1332 enabling selection, isolation,partition and/or grouping of particular sets of power electronicsmodules 1318-1320. The inter-coil AC bus 1308 and the inter-module ACbus 1322 may be connected by a suitable set of coil-module interconnectpathways and switches 1334-1338. The network 1300 switches 1310-1316 and1324-1338 may be controlled by the power electronics modules 1318-1320and/or a system controller 1340 communicatively linked to the powerelectronics modules 1318-1320 by a data bus 1342. Different groupings ofcoils 1302-1306 and/or power electronics modules 1318-1320, anddifferent assignments of such groups, can further expand the dynamicrange of the electric power generation system 100 (FIG. 1), for example,with respect to the range of fluid stream 106 flow rates (and thusturbine 102 and rotor 108 rotation speeds) at which the system 100 cangenerate grid-quality AC.

Each power electronics module 1318-1320, and/or a stator module thatincorporates the power electronics module, may be associated with a datanetwork address (e.g., an internet protocol address), and the systemcontroller 1340 may be located remotely in the data network and/or at aremote physical distance from the power electronics modules 1318-1320.The system controller 1340 may set any suitable parameters of the powerelectronics modules 1318-1320, both individually and collectively.Alternatively, or in addition, functionality of the system controller1340 may be partially or fully distributed among the power electronicsmodules 1318-1320, for example, in accordance with distributed computingtechniques well known to those of skill in the art. The powerelectronics modules 1318-1320 may share status data with each other.Individual power electronics modules 1318-1320 may adjust their settingsbased on status data received from a particular set of neighboring powerelectronics modules 1318-1320. The set of neighbors may be fixed orautomatically determined and/or re-determined, for example, inaccordance with a network peer discovery protocol and/or overlay networkprotocol.

As described above with reference to FIG. 7, high capacity generatorsmay be constructed from stacks of plates of generator modules. FIG. 14is a schematic diagram of an example generator module plate stack 1400in accordance with an embodiment of the invention. The stack 1400includes multiple generator plates 1402-1406 having a common rotor 1408.In the illustrated example, the stator modules 1410-1432 all outputgrid-quality AC 1434, which may be simply routed to the local powergrid. Alternatively, as described above with reference to FIG. 12, DCpower may be routed to a collective inverter or set of inverters toproduce the grid-quality AC 1434.

The description now turns to steps that may be performed in accordancewith an embodiment of the invention. Such steps may be implemented withany suitable number and type of electronic components. Examples ofsuitable electronics components include resistors, capacitors, inductivedevices, semiconductor switching devices such as diodes, thyristors andtransistors, integrated circuits (ICs) including analog ICs and digitalICs such as processors, volatile memory, non-volatile memory, andprogrammable logic devices, switches, excessive current and/or voltageprotection devices, transducers, and optoelectronic devices. Processorsand programmable logic devices may be programmed with any suitableprogramming language and/or computer-executable instructions.

FIG. 15 depicts example steps for generating electric power inaccordance with an embodiment of the invention. At step 1502, one ormore generated power characteristics may be measured. For example, thepower electronics submodule 930 (FIG. 9) may measure one or morecharacteristics of the AC waveform generated in the coil 918 and/or theDC power output from the active rectifier 1214 (FIG. 12). Suchcharacteristics may include amplitude (e.g., amplitude current),frequency and phase of the voltage and/or current waveforms.Alternatively, or in addition, individual power electronics modules1318-1320 (FIG. 13) may provide measurement data to the systemcontroller 1340, and the system controller 1340 may process themeasurement data to take system-level measurements of the generatedelectric power.

At step 1504, one or more desired power characteristics may bedetermined. For example, the power electronics submodule controller 1228(FIG. 12) may determine a desired set of characteristics for the ACwaveform in the coil 918 (FIG. 9) and/or the DC power output from theactive rectifier 1214 based at least in part on the characteristic(s)measured at step 1502, as well as the configuration of the generator 100of FIG. 1 (e.g., coil groupings) and factors such as fluid stream 106flow rate and operating temperature. Again, such characteristics mayinclude amplitude, frequency and phase of the voltage and/or currentwaveforms. At a system level, the system controller 1340 (FIG. 13) maymonitor a ratio of commanded to actually generated current and determinethe ratio of a highest performing generator module to be used as atarget.

One or more intermediate factors may be explicitly determined as part ofdetermined the desired power characteristic(s) of step 1504. Forexample, rotation speeds (e.g., RPM) of the rotor 108 (FIG. 1) and/orthe turbine 102 may be derived from other measurements if not measureddirectly. At step 1506, current turbine rotational speed may bedetermined. For example, the power electronics submodule controller 1228(FIG. 12) may determine the current turbine rotational speed based atleast in part on the generated power characteristic(s) measured at step1502 (e.g., waveform frequency).

At step 1508, a desired turbine rotational speed may be determined. Thepower electronics submodule controller 1228 (FIG. 12) may determine anoptimal turbine rotational speed with respect to a fixed pitch of theturbine 102 and/or a current flow rate of the fluid stream 106 (FIG. 1).For example, the optimal rotational speed of the turbine may be therotational speed that maximizes power capture for the current flow rateand/or effective flow rate of the fluid stream 106. The turbine 102and/or rotor 108 may operate with respect to a torque curve (e.g.,torque generated responsive to changing rotational speed) having a localslope near a current operating point, and the local slope may beadjusted with a counter-torque induced by managing the generated ACwaveform so as to optimize an angle of attack of the turbine 102 bladeswith respect to the fluid stream 106. In an embodiment of the invention,managing turbine rotational speed may have the effect of flattening thetorque and/or power curve and extending the dynamic range of theelectric power generation system 100. There may also be maximumrotational speeds that can be reliably and/or safely sustained in theshort-term and over longer periods, and the desired turbine rotationalspeed may be selected in accordance with these limits and enforced bythe torque control system (i.e., management of the generated ACwaveform).

At step 1510, one or more targets for one or more generated powercharacteristics may be determined. The power electronics submodulecontroller 1228 (FIG. 12) and/or the system controller 1340 (FIG. 13)may determine one or more targets for one or more characteristics of thegenerated AC waveform in the polyphase coil 1204 and/or coil group1302-1306 based at least in part on the desired turbine rotational speeddetermined at step 1508. For example, a phase shift in the generated ACwaveform may magnetically induce a deceleration with respect to therotational speed of the rotor 108 (FIG. 1) and/or turbine 102.

At step 1512, one or more generator modules may be configured to achievethe desired power characteristic(s) determined at step 1504. Forexample, the power electronics submodule controller 1228 may configurethe power electronics submodule 1202 to seek the target(s) determined atstep 1510. In addition, the system controller 1340 may command and/orsignal the power electronics submodule controllers of multiple generatormodules to seek system-level targets. In an embodiment of the invention,coil groups may be configured to achieve the desired powercharacteristic(s). As part of measuring the generated powercharacteristic(s) at step 1502, it may be detected that one or moregenerator modules, or components thereof, have failed, become inactive(e.g., due to hot-unplugging) and/or are performing sub-optimally. Theconfiguration of step 1512 may compensate appropriately, for example, byrerouting AC and/or DC power and/or adjusting individual generatormodule settings to redistribute and/or decrease the generated powerload.

FIG. 16 depicts example steps for configuring generator modules inaccordance with an embodiment of the invention. At step 1602, coilgroups may be determined for a generator. For example, the systemcontroller 1340 (FIG. 13) may partition the generator coils 1302-1306 ofthe stator modules 220-230 (FIG. 2) of the generator 200 into equallysized sets based at least in part on a rotational speed of the rotor 202(e.g., as determined at step 1506 of FIG. 15). At step 1604, powerelectronics modules may be assigned to coil groups. For example, thesystem controller 1340 may assign the power electronics modules1318-1320 to the coil groups determined at step 1602 based at least inpart on expected generated AC waveform characteristics of the determinedcoil groups.

At step 1606, the generation coils 1302-1306 (FIG. 13) may bedisconnected from the power electronics modules 1318-1320, for example,with the coil-module interconnect switches 1334-1338. At step 1608, thecoil selection switches 1310-1316 may be signaled to create the coilgroups determined at step 1602, for example, responsive to commandsand/or signals generated by the system controller 1340. At step 1610,the power module selection switches 1324-1332 may be signaled to changestate in accordance with the power electronics module assignmentsdetermined at step 1604. For example, the power module selectionswitches 1324-1332 may change state responsive to commands and/orsignals generated by the system controller 1340. At step 1612, thegeneration coils 1302-1306 may be reconnected to the power electronicsmodules 1318-1320 in accordance with the power electronics moduleassignments determined at step 1604. For example, the coil-moduleinterconnect switches 1334-1338 may change state responsive to commandsand/or signals generated by the system controller 1340.

FIG. 17 depicts further example steps for configuring generator modulesin accordance with an embodiment of the invention. At step 1702, desiredsystem level generator module settings may be determined, for example,by the system controller 1340 (FIG. 13) as described above withreference to FIG. 15 and FIG. 16. At step 1704, one or more commands maybe sent to one or more generator modules. For example, the systemcontroller 1340 may send the command(s) to configure the generatormodule(s) in accordance with the desired generator module settingsdetermined at step 1702.

Dashed line 1706 indicates that steps 1708-1716 may be performed by eachof the generator module(s) to which commands were sent at step 1704. Atstep 1708, a command may be received. For example, the communicationcomponent 1232 (FIG. 12) of the power electronics submodule 1202 mayreceive the command specifying desired generator module settings sent bythe system controller 1340 (FIG. 13). At step 1710, desired rectifiersettings may be determined. For example, the submodule controller 1228may determine settings for the active rectifier 1214 corresponding tothe desired generator module settings specified in the command receivedat step 1708. At step 1712, desired inverter settings may be determined.For example, the submodule controller 1228 may determine settings forthe inverter 1224 corresponding to the desired generator module settingsspecified in the command received at step 1708. At step 1714, one ormore rectifier controllers may be configured. For example, thecommunication component 1232 may configure the rectifier controller 1234in accordance with the desired rectifier settings determined at step1710. At step 1716, one or more inverter controllers may be configured.For example, the communication component 1232 may configure the invertercontroller 1236 in accordance with the desired inverter settingsdetermined at step 1712.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and/or were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thespecification and in the following claims are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The terms “having,” “including,”“containing” and similar referents in the specification and in thefollowing claims are to be construed as open-ended terms (e.g., meaning“including, but not limited to,”) unless otherwise noted. Recitation ofranges of values herein are merely indented to serve as a shorthandmethod of referring individually to each separate value inclusivelyfalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orclearly contradicted by context. The use of any and all examples, orexemplary language (e.g., “such as”) provided herein, is intended merelyto better illuminate embodiments of the invention and does not pose alimitation to the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to each embodiment of the presentinvention.

Preferred embodiments of the invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the specification. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as explicitly described herein. Accordingly, embodimentsof the invention include all modifications and equivalents of thesubject matter recited in the following claims as permitted byapplicable law.

1. An electric power generation system, comprising: a turbine configuredat least to rotate in a fluid flow, the fluid flow having a varying flowrate, a rotational speed of the turbine based at least in part on theflow rate of the fluid flow; a rotor frame connectively coupled at leastto the turbine such that the rotor frame rotates around an axis ofrotation with a rotational speed corresponding to the rotational speedof the turbine; a plurality of rotor modules connectively coupled atleast to the rotor frame and arranged in one or more rings of rotormodules distributed axially or radially with respect to the axis ofrotation, the plurality of rotor modules collectively configured atleast to generate a magnetic field having at least one characteristicbased at least in part on the rotational speed of the rotor frame; and aplurality of stator modules magnetically coupled to the plurality ofrotor modules and arranged in one or more rings of stator modulescorresponding to the one or more rings of rotor modules, each statormodule incorporating at least one generating coil configured at least togenerate an alternating electric current responsive to the magneticfield and managed to produce a desired magnetically-induced torque thatat least partially controls rotation of the rotor frame.
 2. An electricpower generation system in accordance with claim 1, wherein the fluidflow is wind.
 3. An electric power generation system in accordance withclaim 1, wherein a number of the plurality of rotor modules correspondsto a number of the plurality of stator modules and each pair of rotorand stator modules is incorporated in a corresponding generator module.4. An electric power generation system in accordance with claim 3,wherein each of the rotor modules is paired with a corresponding statormodule and the pair is manufactured, assembled and tested as a unitprior to installation in the electric power generation system.
 5. Anelectric power generation system in accordance with claim 1, wherein aseparation between the plurality of rotor modules and the plurality ofstator modules is maintained substantially with magnetic bearings.
 6. Anelectric power generation system in accordance with claim 1, wherein theturbine is a fixed pitch turbine and the rotational speed of the turbineis controlled independently of a mechanical gearbox.
 7. An electricpower generation system in accordance with claim 6, wherein a magnitudeof the magnetically-induced torque is determined based at least in parton a target rotational speed that is optimal with respect to performanceof the fixed pitch turbine.
 8. An electric power generation system inaccordance with claim 1, wherein the plurality of stator modules actcollectively to cause the magnetically-induced torque and the pluralityof stator modules are configured at least to collectively compensate fora temporary inactivity of one or more of the plurality of statormodules.
 9. An electric power generation system, comprising: a turbineconfigured at least to rotate in a fluid flow, the fluid flow having avarying flow rate, a rotational speed of the turbine based at least inpart on the flow rate of the fluid flow; a plurality of rotor modulesconnectively coupled at least to the turbine, the plurality of rotormodules collectively configured at least to generate a magnetic fieldhaving at least one characteristic based at least in part on therotational speed of the turbine; and a plurality of stator modulesconfigured to collectively, at least: generate at least one alternatingelectric current responsive at least in part to the magnetic fieldgenerated by the plurality of rotor modules; maintain a relativeposition of the plurality of rotor modules with respect to the pluralityof stator modules with magnetic force; and control a rotational speed ofthe turbine with magnetic force.
 10. An electric power generation systemin accordance with claim 9, wherein controlling the rotational speed ofthe turbine comprises controlling at least one characteristic of said atleast one alternating electric current generated by the plurality ofstator modules.
 11. An electric power generation system in accordancewith claim 10, wherein each of the plurality of stator modules comprisesan active rectifier and controlling said at least one characteristic ofsaid at least one alternating electric current comprises modifying saidat least one characteristic with at least one active rectifier.
 12. Anelectric power generation system in accordance with claim 9, furthercomprising a system control module configured at least to coordinateindividual stator module participation with respect to control of therotational speed of the turbine.
 13. An electric power generation systemin accordance with claim 9, wherein each of the plurality of statormodules comprises a generator coil with a plurality of tap points thatare dynamically selectable with switches.
 14. An electric powergeneration system in accordance with claim 9, wherein each of theplurality of rotor modules comprises a permanent magnet fastened to aframe of the rotor module with a flexible coupling that allows movementof the permanent magnet with respect to the frame in a directionparallel to a main magnetic flux path.
 15. An electric power generationsystem in accordance with claim 9, wherein each rotor module comprisesat least one stabilization magnet, each stator module comprises at leastone corresponding stabilization magnet, and the stabilization magnetsact collectively to keep stable a separation between the plurality ofrotor modules and the plurality of stator modules.
 16. A method ofgenerating electric power, comprising: measuring at least one value ofat least one characteristic of a plurality of rotor modules rotatingaround an axis, the rotating rotor modules generating an alternatingelectric current in at least one generating coil of at least one statormodule; determining at least one value of at least one characteristic ofat least one signal controlling the alternating electric current basedat least in part on said at least one value of said at least onecharacteristic of the plurality of rotor modules and a target speed ofrotation of the plurality of rotor modules around the axis; andconfiguring said at least one stator module at least to control thealternating electric current in accordance with said at least onesignal, said at least one stator module arranged with respect to theplurality of rotor modules such that modifying the alternating electriccurrent modifies a speed of rotation of the plurality of rotor modulesaround the axis.
 17. A method in accordance with claim 16, wherein theplurality of rotor modules are connectively coupled to a turbine thatcauses the plurality of rotor modules to rotate around the axis with thespeed of rotation and said at least one value of said at least onecharacteristic of the plurality of rotor modules corresponds to a speedof rotation of the turbine.
 18. A method in accordance with claim 16,wherein configuring said at least one stator module comprisesconfiguring a plurality of groups of generating coils among a pluralityof stator modules based at least in part on said at least one measuredvalue of said at least one characteristic of the plurality of rotormodules.
 19. A method in accordance with claim 16, wherein measuringsaid at least one value of said at least one characteristic of theplurality of rotor modules comprises measuring a plurality of valuescorresponding to characteristics of alternating electric currents ingenerating coils of a plurality of stator modules, and configuring saidat least one stator module comprises configuring each of the pluralityof stator modules to modify the alternating electric current in agenerating coil of the stator module based at least in part on thecorresponding characteristic value.
 20. A method in accordance withclaim 19, wherein the modification of the alternating electric currentin each of the generating coils of the plurality of stator modules isfurther based at least in part on the plurality of measuredcharacteristic values.